haskell.nix/README.md

haskell.nix is infrastructure for building Haskell packages with Nix

haskell.nix can automatically translate your Cabal or Stack project and its dependencies into Nix code.

Documentation

Getting started

a) Using cabal.project

Add a default.nix:

let 
  # Fetch the latest haskell.nix and import its default.nix
  haskellNix = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {};

  # haskell.nix provides access to the nixpkgs pins which are used by our CI, hence
  # you will be more likely to get cache hits when using these.
  # But you can also just use your own, e.g. '<nixpkgs>'
  nixpkgsSrc = haskellNix.sources.nixpkgs-2003;

  # haskell.nix provides some arguments to be passed to nixpkgs, including some patches
  # and also the haskell.nix functionality itself as an overlay.
  nixpkgsArgs = haskellNix.nixpkgsArgs;
in
{ pkgs ? import nixpkgsSrc nixpkgsArgs
, haskellCompiler ? "ghc865"
}:

# 'cabalProject' generates a package set based on a cabal.project (and the corresponding .cabal files)
pkgs.haskell-nix.cabalProject {
  # 'cleanGit' cleans a source directory based on the files known by git
  src = pkgs.haskell-nix.haskellLib.cleanGit { name = "haskell-nix-project"; src = ./.; };
  compiler-nix-name = haskellCompiler;
}

Note that you'll need to add a comment specifying the expected sha256 output for your source-repository-packages in your cabal.project file:

source-repository-package
  type: git
  location: https://github.com/input-output-hk/iohk-monitoring-framework
  subdir:   plugins/backend-editor
  tag: 4956b32f039579a0e7e4fd10793f65b4c77d9044
  --sha256: 03lyb2m4i6p7rpjqarnhsx21nx48fwk6rzsrx15k6274a4bv0pix

b) Using stack.yaml

Add a default.nix:

let 
  haskellNix = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {};
  nixpkgsSrc = haskellNix.sources.nixpkgs-2003;
  nixpkgsArgs = haskellNix.nixpkgsArgs;
in
{ pkgs ? import nixpkgsSrc nixpkgsArgs
}:
pkgs.haskell-nix.stackProject {
  src = pkgs.haskell-nix.haskellLib.cleanGit { src = ./.; };
}

Working with a project

To build the library component of a package in the project run:

nix build -f . your-package-name.components.library

To build an executable:

nix build -f . your-package-name.components.exes.your-exe-name

To open a shell for use with cabal run:

nix-shell -A shellFor
cabal new-build your-package-name
cabal new-repl your-package-name:library:your-package-name

Using a binary cache

To use precompiled binaries you'll need:

• To configure the IOHK binary cache by following the instructions on iohk.cachix.org.
• To pin your nixpkgs to match one of the revisions built by our CI: these can be found inside the sources attribute (see the quickstart above for an example).

Related repos

The haskell.nix repository contains the runtime system for building Haskell packages in Nix. It depends on other repos, which are:

• nix-tools — provides the programs for generating Nix expressions from Haskell projects.

• hackage.nix — the latest contents of the Hackage databases, converted to Nix expressions.

• stackage.nix — all of the Stackage snapshots, converted to Nix expressions.

IRC Channel

Join the #haskell.nix channel on irc.freenode.net to get help or discuss the development of haskell.nix and nix-tools.